Identification
This tiny marvel, rarely exceeding 15mm in length, looks like a miniature, shaggy rug lost at sea. Its translucent white or cream body is densely covered in long, finger-like papillae (villi) that give it a distinctively "hairy" silhouette. To distinguish it from its cousins, look for the brilliant orange or reddish-orange tips on each papilla, which look like tiny glowing embers. Unlike the smooth, gelatinous feel of many nudibranchs, *Aegires villosus* has a rigid, almost crunchy posture. A key field mark is the trio of leaf-like gills located on the back, protected by a prominent, overhanging lobe that looks like a small shelf.
Habitat & Range
A true citizen of the tropical Indo-West Pacific, this species is found from the Red Sea and Tanzania to the Philippines and Hawaii. It is a creature of the reef, specifically favoring shallow, sun-drenched coral gardens and rocky slopes. You won’t find them in the open; they prefer the "micro-wilderness" of coral rubble and dark crevices where their specific food sources flourish.
Behaviour
Patience is a virtue when tracking this slug. They are slow-moving and highly cryptic, often perfectly camouflaged against the textured backdrop of the reef. Solitary by nature, they spend their days methodically crawling over the substrate. When threatened, they don’t possess a "flight" response; instead, they cling tightly to the rock, relying on their stiff, prickly texture to make themselves an unappealing snack for passing fish.
Diet
*Aegires villosus* is a specialist with a very narrow palate. It feeds exclusively on calcareous sponges, particularly those in the genus *Leucetta*. Using a specialized, tooth-lined ribbon called a radula, it rasps away at the sponge’s tough, mineral-rich surface, effectively "grazing" on the living tissue.
Fascinating Fact
While most sea slugs are soft and squishy, *Aegires villosus* is reinforced with "sclerites"—tiny, needle-like calcified structures embedded throughout its skin. This gives the slug a sandpaper-like texture, essentially turning its entire body into a suit of living chainmail!